#include<stdio.h>
int main()
{
	int n,m,i;
	double a,sum[1001],p[1001],f[1001],min=29999; 
		scanf("%d%d",&n,&m);
		scanf("%lf",&a);
		for(i=0;i<n;i++)
		{
			scanf("%lf%lf",&p[i],&f[i]);
			if(f[i]>=m)
				sum[i]=p[i];
			else
				sum[i]=p[i]+a*(m-f[i]);
			if(min>sum[i])
				min=sum[i];
		}
		printf("%.0lf\n",min);
	return 0;
}
